Yeah volume is definitely important. Also I would work on a lot of static holds, with your dumbbells. As simple as when your in the down position of any of your exercises, just hold the weight, with forearm extended and open as long as you can hold before curling back up. This works great on the edge of a table, holding the dumbbell, like your arm wrestling it, preventing it from taking you down, and time it. Try to increase that static hold time. Also a good way to work on static hold in the up position, are static hold chin-ups. Static holds are one of the best ways to increase your stamina and endurance in your arms. You’ll find great stamina can help win a lot of matches.
Early on I used to do great, and win a lot in early rounds, and then I would start to wear down. I had a lot of strength and power, so I would try to overwhelm my opponent with speed and exploding out the gate. That was great until you had an opponent that could weather the storm, hold you up and try to wear on you. That’s inevitably when I would lose. So I worked on my stamina and got to where I could hold an opponent and start wearing them down. The farther you get in this sport, the more you will need that endurance.